This paper analyzes the effects of changing age structure and family size on schooling in Brazil. Cohorts born before 1982 were born during a period of falling family size but increasing cohort size. We show that the growth of the school-aged population peaked around 1990, coinciding with the onset of increasing enrollment rates in the 1990s. Pooling household survey data from 1977 to 1999, we estimate the effect of family size, cohort growth, and parental schooling on school enrollment. All have effects in the predicted directions, with the combined variables explaining over 70% of increased enrollment over the period.